The term “microfluidic” refers to a system or device having one or a network of chambers and/or channels, which have micro scale dimensions, e.g., having at least one cross sectional dimension in the range from about 0.1 μm to about 500 μm. The volume handled is in the range of nanolitre, that is less than 5000 ηl, generally less than 1000 ηl. Microfluidic substrates are often fabricated using photolithography, wet chemical etching, injection-molding, embossing, and other techniques similar to those employed in the semiconductor industry. The resulting devices can be used to perform a variety of sophisticated chemical and biological analytical techniques.
Microfluidic analytical systems have a number of advantages over conventional chemical or physical laboratory techniques. For example, microfluidic systems are particularly well adapted for analyzing small sample sizes, typically making use of samples on the order of nanoliters and even picoliters. The channel defining substrates may be produced at relatively low cost, and the channels can be arranged to perform numerous analytical operations, including mixing, dispensing, valving, reactions, detections, electrophoresis, and the like. The analytical capabilities of microfluidic systems are generally enhanced by increasing the number and complexity of network channels, reaction chambers, and the like.
Substantial advances have recently been made in the general areas of flow control and physical interactions between the samples and the supporting analytical structures.
Flow control management may make use of a variety of mechanisms, including the patterned application of voltage, current, or electrical power to the substrate (for example, to induce and/or control electrokinetic flow or electrophoretic separations). Alternatively, fluid flows may be induced by capillarity attraction or mechanically through the application of differential pressure, acoustic energy, or the like. Selective heating, cooling, exposure to light or other radiation, or other inputs may be provided at selected locations distributed about the substrate to promote the desired chemical and/or biological interactions. Similarly, measurements of light or other emissions, electrical/electrochemical signals, and pH may be taken from the substrate to provide analytical results. As work has progressed in each of these areas, the channel size has gradually decreased while the channel network has increased in complexity, significantly enhancing the overall capabilities of microfluidic systems.
The microfluidics technologies/devices are capable of controlling and transferring tiny quantities of liquids to allow biological assays to be integrated and accomplished on a small scale.
Microfluidics is the miniaturization of biological separation and assay techniques to such a degree that multiple “experiments” can be accomplished on a “chip” small enough to fit in the palm of your hand. Tiny quantities of solvent, sample, and reagents are steered through narrow channels on the chip, where they are mixed and analyzed by such techniques as electrophoresis, fluorescence detection, immunoassay, or indeed almost any classical laboratory method.
Today a number of products varying in many respects are available. Laboratory chips may be made from plastic, glass, quartz or even silicon. The fluid may be driven by centrifugal forces, mechanical pressure or vacuum pumps, by inertia, or by one of several electrical methods; fluid flow can be diverted around the chip by mechanical valves, surface tension, voltage gradients, or even electromagnetic forces.
In the technique of using centrifugal forces to drive the fluid a disc that can be spinned is used. Some discs have been of the same physical format as conventional CDs. Samples may be placed in an inner position of the disc and centrifugal forces, created as the disc rotates, push them out through channels cut into the plastic, circumventing the need to design sophisticated electrokinetic or mechanical pumping structures.
As will become evident in the forth-coming description the present invention is in particular applicable to (but not limited to) micro-analysis systems that are based on micro-channels formed in a rotatable, usually plastic, disc, often called a “lab on a chip”. Such discs can be used to perform analysis and separation on small quantities of fluids. In order to reduce costs it is desirable that the discs should be not restricted to use with just one type of reagent or fluid but should be able to work with a variety of fluids.
Furthermore it is often desirable during the preparation of samples that the disc permits the user to dispense volumes of any desired combination of fluids or samples without modifying the disc. A microanalysis device for fluids provided in a rotatable disc is described e.g. in WO-0146465.
All analytical procedures are performed with the purpose of generating information that is requested or required for further decisions. In order to be useful, information need to fulfill certain quality goals. Low quality assays require often several replicates in order to generate useful information and is more costly to run for the customer. These may differ very much on the process and the consequence of decisions made on inappropriate information.